Henry Moseley (1887-1915): A British chemist, Henry Moseley studied
under Rutherford and brilliantly developed the
application of X-ray spectra to study atomic structure; Moseley's discoveries resulted in a more
accurate positioning of elements in the Periodic Table
by closer determination of atomic numbers. Tragically for the development of science,
Moseley was killed in action at Gallipoli in 1915.

In 1913, almost fifty years after Mendeleev, Henry Moseley published the results of his
measurements of the wavelengths of the X-ray spectral lines of a number of elements which
showed that the ordering of the wavelengths of the X-ray emissions of the elements
coincided with the ordering of the elements by atomic number. With the discovery of
isotopes of the elements, it became apparent that atomic weight was not the significant
player in the periodic law as Mendeleev, Meyers and others had proposed, but rather, the
properties of the elements varied periodically with atomic number.

When atoms were arranged according to increasing atomic number, the few problems
with Mendeleev's periodic table had disappeared. Because of Moseley's work, the modern
periodic table is based on the atomic numbers of the elements.